Materials such as soil samples for volatile organic compound (VOC) analysis are usually shipped to a testing lab in coolers with ice packs such that they are kept at refrigerator temperatures near 4 C (+/−2 C). However, both the EPA and ASTM recognize the benefit of shipping samples at cooler temperatures—freezer (also known as freezing) temperatures (−7 to −17 C)—for preservation. Known systems for achieving such temperature control are often impractical or simply not feasible: shipping samples from the field in freezer compartments with electronic cooling devices powered by batteries is not feasible in most cases; shipping in coolers with dry ice is also not a viable option because air shipment of packages containing dry ice is regulated (dry ice sublimes to gaseous carbon dioxide, which can displace air in sealed aircraft). Also, dry ice has a temperature of −78 C, which is so cold that it will cause the seals of the sample containers to be compromised, and VOC's will be lost. Aspects of this inventive technology may resolve one or more of these problems through the use of a system that includes cooled packs of an aqueous solution of salt in combination with a cooler that may be adapted to enhance thermal insulation of enclosed contents. Some aspects may be directed to a novel water/salt solution alone.